The fatty acid alkyl ester sulfonate metal salt (hereinafter also referred to as “MES”) is widely used as a surfactant for producing granular detergent compositions for clothes. A variety of production methods for granular detergent compositions are known, and dry-blending of the MES powder with another surfactants, builders and the like, spray-drying and the like are typical examples of the production method.
When the MES is subjected to dry-blending, the MES in a paste form is once concentrated into a solid form, and the solid is then crushed. When a granular detergent composition is produced by the spray drying method using the MES, it is common practice to form a detergent slurry by mixing the MES in a paste form containing a considerable water content with the builders and the like. In such cases, dry-blending of powders or preparation of detergent slurry is often carried out at a place far from the site where the MES paste has been produced. Namely, it may be required to transport the MES in a paste form not only within Japan, but also to the foreign countries. The cost of transporting the MES in a paste form is high. The MES in the form of a concentrate can be transported more economically. There are some known methods for concentrating the MES (Japanese Patent Unexamined Publication (hereinafter referred to as “JP Kokai”) No. 2004-210807, National publication of PCT application 2004/111166, JP Kokai No. 2003-105396, and JP Kokai No. 2003-82395).
When the concentrate in a solid state is transported, however, the solid will tend to produce cakes under the circumstances of heavy load or high temperature, which makes it difficult to take the concentrate out of the container. In addition, when the caking takes place in the concentrate, the pulverizing process or the process of reconstituting to a paste will be hindered if the process is carried out at the place where the concentrate has been transferred. This means deterioration of the handling properties.
To produce the granular detergent composition, which is constructed of a surfactant, zeolite, alkali chemical, dye and the like, a pulverizing step is often provided for the purpose of sizing to improve the fluidity and the appearance after the granulation step.
The fatty acid alkyl ester sulfonate metal salt (MES) is widely used as a surfactant for constituting the granular detergent composition. When the MES powder is prepared, the pulverizer is operated, generally with cold air of less than 30° C. being blown into the pulverizer to prevent the powder from adhering to the pulverizer (for example, as in National publication of PCT application 2004/111166).
However, the MES powder obtainable by the above-mentioned method shows a broad particle size distribution including high amounts of coarse powders and fine powders. With high content of coarse powders, the problem of low water solubility is produced. High content of fine powders also produces the problem of low water solubility because of the formation of cakes during the storage.
In contrast to this, the powder with a narrow particle size distribution, i.e., containing smaller amounts of coarse powders and fine powders can reduce the occurrence of the above-mentioned problems. In addition to the above, the powder with a narrow particle size distribution can be blended with inorganic powders such as zeolite and the like without classification, which is considered to be industrially advantageous.